A DNA nicking-closing enzyme encapsidated in vaccinia virus: partial purification and properties.

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Abstract
Vaccinia virus cores contain an activity which can relax left- and right-handed superhelical DNA. This virus-specific nicking-closing enzyme was highly purified and differs from the corresponding host [human cervical carcinoma HeLa cell] enzyme in salt optimum, in sedimentation coefficient and in polypeptide composition as determined on sodium dodecyl sulfate/polyacrylamide gels. The enzyme is probably newly synthesized after the cessation of host protein synthesis which follows virus infection. The most highly purified preparation contains 2 polypeptides, one of MW 24,000 and the other 35,000. The former polypeptide is a major constituent of the virus (7% of total protein by wt), but the latter is present in a much smaller amount (0.2%). Chromatography with denatured DNA-cellulose reveals that the activity is predominately associated with those fractions enriched in the polypeptide of greater MW.